Paper 2 Practicals

Question 1

Internal resistance of cell

Answer 1

Equipment:
* Cell
* Voltmeter
* Ammeter
* Variable resistor
* Switch
Method:
* Variable resistor max resistance
* Close switch, record voltage and ammeter
* Open switch, change resistance and record new results
Calculations::
* Draw graph of V against I, gradient is -r

Question 2

Max power of cell

Answer 2

Equipment:
* Battery
* Ammeter
* Voltmeter
* Variable resistor
Method:
* Record terminal voltage for 8 different current values by changing variable resistor
Calculations:
* Power supplied = V*I
* Resistance = V/I
Method:
* Plot graph of power against resistance – max power = peak. Peak power happens when resistance = internal resistance of cell.

Question 3

Resistivity of a wire practical

Answer 3

Equipment:
* Cell
* Ammeter
* Resistor
* Voltmeter across wire
Method:
* Measure diameter of wire with micrometer screw gauge at multiple points to find mean.
* Measaure p.d.
* Measure current
* Measure length with a ruler.
* Vary length with equal intervals to get 8 points by changing crocodile clip connection.
Calculation:
* Graph of R against L
* Gradient = p/A

Question 4

Measuring wavelength of light using double slit

Answer 4

Method:
* Measure distance from slit to screen, D with ruler.
* Measure a with travelling microscope or calculate it as (1/diffraction grating (mm) x 10^-3)
* Vary distance D and measure x with rule, keep light source constant.
Calculation:
* Plot a graph of x against D, gradient = λ /slit separation
Measuring speed of sound

Question 5

Polarisation of waves

Answer 5

Method:
* Microwaves absorbed when grille wires are parallel to vibrations of microwaves.
* Attach voltmeter to microwave receiver.
* Microwaves are transmitted when the direction of vibration of EM field and the wires are perpendicular. This corresponds to high voltmeter reading.

Question 6

Planck’s constant

Answer 6

Equipment:
* Cell, variable resistor and diode in series
* Votmeter in parallel to diode
Method:
* Vary P.D. across LED by varying resistance until it lights up, V = threshold voltage
* Wavelength of LED is given by manufacturer
* Repeat for multiple LED of different wavelength
Calculations:
* Plot graph of V against 1/λ
* eV = hc/λ
* V=hc/e * 1/ λ

Question 7

Electromagnetic motor effect

Answer 7

Method:
* Current flows through the wire between magnet, wire will experience a force
* Due to newtons third law, and equal and opposite force will be acted on the magnet on the weighing balance.
* Place horsehoe magnet on weighing balance and hit zero.
* Vary resistance with variable resistor to change I.
* Place wire inbetween horshoe magnet, F=mg on the balance where m is the mass on balance when wire pushes on magnet.
Investigating magnetic field
Method:
* Attach search coil to data logger with known turns
* Move coil in and out of field, use data from data logger to plot EMF induced against time
* Area = flux linkage

Question 8

Discharging and charging a capacitor

Answer 8

Equipment:
* Power supply
* Switch 1, resistor, capacitor in series.
* Switch 2 in parallel to resistor and capacitor
* Voltmeter in parallel to ONLY the capacitor.
Method:
* Close switch 1 with power supply on to charge capacitor
* Close switch 2 to discharge.
* Measure p.d. across capacitor in equal intervals of time as the capacitor discharges.
* Plot graph of ln(v) against t.
* Gradient = -1/CR

Question 9

Investigating half life

Answer 9

Method:
* Measure background countrate without source.
* Number of particles per second = count rate/time interval. Do it every 10 seconds for 5 minutes.
* Repeat the above for radioactive source, every 10 seconds for 5 minutes.
* Subtract back ground reading for each reading of radioactive substance.
* Half life = ln2/decay constant
* Or, plot graph of counts vs time, when counts half the corresponding time = half life.